Electrically conductive alloy



United States Patent 3,254,992 ELECTRICALLY CONDUCTIVE ALLOY Albert Ericson, Central Falls, R.I., assignor to Garde Manufacturing Company, Cumberland, R.I., a'corporation of Rhode Island N0 Drawing. Filed Nov. 8, 1962, Ser. No. 236,409 5 Claims. (Cl. 75-134) My present invention relates to the metallurgical art and more particularly to a novel alloy which is corrosion resistant and has electrical conductivity approaching copper alloys.

Modern electronic circuits are normally divided with hundreds and sometimes thousands of electrical connections. To reduce the overall resistance of the unit and minimize changes in resistance due to corrosion, it is highly desirable that the electrical connectors remain clean and highly conductive. Since the finest conductor known is silver, it is customary that the electrical connectors that are used are stamped from brass or steel and then plated with silver. However silver is corrosive and loses its ability to transmit easily from its surface. It is therefore necessary to then plate the silver with gold to cut down on the corrosion. Since the gold is terribly expensive the amount of gold plated over silver is usually in the nature of millionths of an inch in thickness. Furthermore, the silver is known to migrate through the gold plate and then corrode the surface.

The present invention is designed to overcome the difficulties heretofore encountered by providing a metallic alloy having all the properties required of a good electrical contact including high conductivity very close to that of copper alloys and extremely high corrosion resistance. The alloy of the present invention can thus be used as a plating medium for over plating the basic brass or steel materials, or sheet, rod, etc., and contacts may be made entirely of the new alloy material.

The basis of the present invention is an alloy of indium. In and of itself indium is corrosive and subject to attack by oxidation, by nitrates, by the chlorides, etc. It is also a poor electrical conductor being number 26 on the list after silver. Furthermore indium is almost as soft as lead and this softness is undesirable in certain applications. It has heretofore been known that the addition of phosphorous to indium tends to make the indium corrosion resistant in some degrees. Applicant has discovered that the addition of phosphorous together with pure silver and pure copper produces an alloy having highly desirable properties Which the base metal indium does not have. For example applicant has found that an alloy of indium phosphorous silver and copper becomes highly corrosion resistant, much better than that of indium and phosphorous alone. It is highly resistant to a concentrated nitric acid atmosphere, to a 20% solution of potassium sulfide, to a 30% solution of hydrogen peroxide and to a 40% solution of sodium chloride. Thus tests have shown that the new alloy is corrosion resistant to a great degree to all the more caustic elements to which it could be subject. Furthermore, the conductivity of the new alloy would place it near copper alloys. The applicant has also found that the new alloy is much harder than the original metal and that the hardness of the alloy can be controlled by the process of preparation.

Furthermore, indium has certain lubricating qualities inherent in the crystal structure of the metal. Applicant has found that the new alloy retains some of the indiums lubricating qualities. This is essential to reduce friction and wear for contacts and bearings. Applicant has found that for an electrical contact the new alloy performs equal to or better than the gold plate over silver and/ or nickel and costs very much less.

3,254,992 Patented June 7, 1966 ice The alloy of indium phosphorous silver and copper can be prepared in rods, sheets, strips or in any desirable manner and can be prepared in any desirable hardness. Applicant preferably uses silver prepared from AR grade silver nitrate heated in a furnace at 1900 F. until pure silver is left. The copper is preferably iron free.

As an example of one form of alloy prepared by the present invention, the applicant mixed 60 grams of indium with 6 grams of phosphorous in a stainless steel chamber in a 30 inch mercury vacuum for thirty minutes. The vacuum chamber was then filled with argon gas under 42 pounds pressure. The indium phosphorous mixture was then heated 2800 F. with an induction furnace for one hour. It was then cooled in room ambient until it reached room temperature. I then mixed twenty grams of silver with 2.5 grams of copper liquefied 1900 F. in an oxidizing atmosphere. The premelt of indium and phosphorous was then added to the liquid alloy of copper and'silver and I continued to heat at 1900 F. until the entire mass is liquid, stirring it with a carbon rod. The alloy can then be poured into a mold for any desired shape or for further Working.

In the above example the various ingredients are approximately in the following percentages:

Indium 60 gr.=67% Phosphorous 6 gr.=7% Silver 20 gr.=23% Copper 25 gr.=3% Total 88.5 gr.=l00% The resulting alloy will be found to be highly corrosive resistant to nitric acid, potassium sulfide, hydrogen peroxide, or salt and have a high electrical conductivity. The metal will plate easily over most metals.

It may be desirable to roll the metal for stamping purposes or to prepare the metal in different forms. For this purpose the proportions of silver and copper may of course be varied to suit the different requirements. Basically there must be enough phosphorous in the mixture to take care of the silver and copper so that increases or decreases in the silver and copper content will be reflected in the phosphorous content.

The alloy of the present invention can also be plated on various bases by making it the anode of a conventional plating tank in which the plating solution comprises a saturated solution of sulfamic acid (NH SO H) buffered with 5 grams of thiourea and 2 grams of dextrose per 1000 milliliters of acid.

I have thus prepared a new alloy comprising indium together with phosphorous, silver and copper, the new alloy having a high corrosion resistance and excellent conductivity. Other advantages of the present invention will be readily apparent to a person skilled in the art.

I claim:

1. An alloy of indium having corrosion resistance and good electrical conductivity consisting of approximately 67% indium and a mixture of phosphorous, silver and copper constituting approximately 33% of the alloy.

2. An alloy of indium having corrosion resistance and good electrical conductivity consisting of approximately 67% indium, 7% phosphorous and a mixture of silver and copper constituting approximately 26%.

3. An alloy of iridium having corrosion resistance and good electrical conductivity consisting of approximately 67% indium, 7% phosphorous, 23% silver and 3% copper.

4. An alloy of indium as in claim 2 wherein the percentage of indium is fixed and wherein the percentages of phosphorous and silver and copper may be varied whereby an increase of silver and copper requires'a decrease in phosphorous and a decrease in silver and copper requires an increase in phosphorous.

5. An alloy of indium as in claim 3 wherein the percentage of indium is fixed and wherein the relative percentages of phosphorous, silver and copper may be varied to equal approximately 33%.

References Cited by the Examiner UNITED STATES PATENTS 2,049,291 7/1936 Comstock 75135 2,050,387 8/1936 Scott 75135 2,460,252 1/1949 Du Rose et a1 204-43 10 2,649,368 8/1953 Smith et a1 75--l34 2,680,071 6/1954 Epstein et a1. 75134 4 2,905,601 9/ 1959 Rinkeret a1. 204-43 2,929,859 3/1960 Loferski 148-1.5 3,092,591 6/1963 Jones et a1 252518 OTHER REFERENCES Properties of Elemental and Compound Semiconductors, Metallurgy Society Conf. AIME, vol. 5, 1960, pp. 59-64.

DAVID L. RECK, Primary Examiner. HYLAND BIZOT, BENJAMIN HENKIN, Examiners. D. L. REISDORF, R. O. DEAN, Assistant Examiners. 

1. AN ALLOY OF INDIUM HAVING CORROSION RESISTANCE AND GOOD ELECTRICAL CONDUCTIVITY CONSISTING OF APPROXIMATELY 67% INDIUM AND A MIXTURE OF PHOSPHOROUS, SILVER AND COPPER CONSTITUTING APPROXIMATELY 33% OF THE ALLOY. 